The present invention relates to a process and to an apparatus for implanting particles in a solid. It is more particularly applied in the doping of semiconductors, especially for constructing MOS transistors and low value resistors in bipolar circuits.
A known method for implanting particles in a solid is ion implantation. In this case, the ions of the species which it is wished to implant in the solid are produced in an ion source. This is followed by the production of a beam of said ions which is accelerated to give it the necessary energy level for penetrating the solid.
An important disadvantage of this method is that it is difficult to obtain a pure ion beam, i.e. an ion beam containing only the ions to be implanted in the solid. Thus, the ion source, which produces the ions, e.g. in a conventional manner by an electrical discharge in a gas, produces in a random manner the ions of the species which it is wished to implant in the solid, together with other ions. It is then necessary to sort the ions produced, in order only to accelerate those which it is wished to implant in the solid.
A known process based on ion implantation is recoil implantation. In this method, the solid is covered with a thin coating of the element which it is wished to implant there. A beam of high-energy primary particles, e.g. argon ions is then directed towards the solid. These high-energy primary particles collide with the atoms on the thin coating and transfer thereto their energy, which enables the atoms of the thin coating to penetrate the solid.
This recoil implantation method is mainly limited by ion erosion of the thin coating deposited on the solid as implantation takes place. This disappearance of the coating limits the doses of particles which can be implanted in the solid.